1. Field of the Invention
The present invention is generally related to broadband communications systems. More particularly, the present invention is related to a cable modem termination system (CMTS) in a broadband communications system.
2. Background Art
In broadband communications architectures, data is transferred between a central location and many remote subscribers. For broadband cable modem systems, the central location may be referred to as a headend and the remote subscriber equipment is referred to as a cable modem (CM). In cable modem systems, the communication path from the headend to the cable modem is called the downstream and the communication path from the cable modem to the headend is called the upstream.
As cable modem systems introduce new services, new ways to increase network capacity at a reasonable cost to the subscriber must be implemented. Thus, cable modem systems are constantly being reconfigured to provide adequate bandwidth to remote subscribers.
A cable modem system is typically housed in a hybrid fiber/coaxial (HFC) plant (also referred to as a HFC system). The hybrid fiber/coaxial plant consists of a fiber portion and a coaxial portion. The headend is housed in the fiber portion of the hybrid fiber/coaxial plant. A Cable Modem Termination System (CMTS), located within the headend, services a plurality of cable modems, located in the coaxial portion of the HFC plant via a plurality of fiber nodes in a point-to-multipoint topology. The network over which the CMTS and the cable modems communicate is referred to as a hybrid fiber/coaxial cable network.
Typically, bandwidth is available to transmit signals downstream from the headend to the cable modems. However, in the upstream, bandwidth is limited and must be arbitrated among the competing cable modems in the system. Cable modems request bandwidth from the CMTS prior to transmitting data to the headend. The CMTS allocates bandwidth to the cable modems based on availability and the competing demands from other cable modems in the system.
In the coaxial portion of the hybrid fiber/coaxial plant, problems may arise with the coaxial cable. Such problems may include loose connectors, poor shielding, and similar points of high impedance. These problems cause noise signals to develop from interference sources such as radio transmissions, electric motors, and other sources of electrical impulses. The point-to-multipoint topology of the cable modem system complicates upstream transmissions by exacerbating the noise. With the multipoint structure of the HFC system, noise is additive in the upstream. Thus, the noise problem is more intense in the upstream as signals approach the headend.
One method of providing additional bandwidth to any one cable modem in the hybrid fiber/coaxial plant requires the fiber node servicing that cable modem to be split. Depending on the frequency stacking in the HFC plant, more upconverters may be required to service the new fiber node resulting from the split. Since all of the signals are combined at the headend, there is a limit to the number of times fiber nodes can be split without causing additional noise sources to enter the system. This makes the CMTS in the headend architecture difficult to expand into available fiber bandwidths.
What is therefore needed is a system and method for maximizing bandwidth allocations to cable modems while minimizing system noise in a HFC plant.